Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
In operation, the magnetic disk is normally driven by the contact start stop (CSS) method, wherein the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. The magnetic head unit is arranged such that the head can be freely moved in both the circumferential and radial directions of the disk in this floating state allowing data to be recorded on and retrieved from the surface of the disk at a desired position.
Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from a stop and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in.sup.2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times (.times.) the linear density (BPI) in terms of bits per inch. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head. However, another factor operates against that objective. If the head surface and recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces eventually leading to what is referred to as a "head crash." Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
In order to satisfy these competing objectives, the recording surfaces of magnetic disks are conventionally provided with a roughened surface to reduce the head/disk friction by techniques referred to as "texturing." Conventional texturing techniques involve polishing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer which is typically chromium or a chromium-alloy, a magnetic layer, a protective overcoat which typically comprises carbon, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated on the surface of the magnetic disk.
A typical magnetic recording medium is depicted in FIG. 1 and comprises a substrate 10, typically an aluminum (Al)-base alloy, such as an aluminum-magnesium (Al--Mg) alloy, plated with a layer of amorphous nickel-phosphorous (NiP). Substrate 10 typically contains sequentially deposited thereon a chromium (Cr) underlayer 11, a magnetic layer 12 which is usually a cobalt (Co)-base alloy, a protective overcoat 13 which usually comprises carbon, and a lubricant topcoat 14. Cr underlayer 11, Co-base alloy magnetic layer 12 and protective carbon overcoat 13 are typically deposited by sputtering techniques. A conventional Al-alloy substrate is provided with a NiP plating primarily to increase the hardness of the Al substrate, serving as a suitable surface on which to provide the requisite surface roughness or texture, which is substantially reproduced on the disk surface.
The escalating requirements for high areal recording density impose increasingly greater requirements on thin film magnetic media in terms of coercivity, squareness, low medium noise and narrow track recording performance. In addition, increasingly high density and large-capacity magnetic disks require increasingly small flying heights, i.e., the distance by which the head floats above the surface of the disk in the CSS drive. The requirement to further reduce the flying height of the head imposed by increasingly higher recording density and capacity render it particularly difficult to satisfy the requirements for controlled texturing to avoid head crash.
The conflicting requirements for minimum transducer flying height and texturing can be alleviated to some extent by providing a separate landing or CSS zone and a separate data zone. In this way, the surface of the data zone can be optimized for data storage and retrieval, while the landing zone can be optimized for texturing to satisfy the CSS requirements. Such a textured surface comprising a head landing zone and a data recording zone can be produced by initially polishing the surface and then laser texturing to form the head landing zone leaving a polished data zone. However, the resulting surface would contain undesirable abrupt topographical changes between the landing zone and the data zone.
Abrupt topographical changes on the surface of a magnetic recording medium adversely affect the flying stability and glide performance of magnetic recording heads, and detrimentally affect the reliability of the head-medium interface. Moreover, such problematic local abrupt profile changes require greater precision in texturing.
Accordingly, there exists a need to provide a textured surface for high areal recording density having a data zone optimized for data recordation and retrieval, and a landing zone having topography optimized for CSS operation, without abrupt topographical changes between the data zone and the landing zone.